Storage system

ABSTRACT

For using a plurality of files contained in one logical device with a plurality of processing systems, sharing of a data storage unit among the plurality of processing systems is realized without need for a host processing system to check use states of the files in a server storage unit. Information concerning extent (extent range) of an input/output processing request issued by a host processor is stored in a control memory incorporated in a control unit for allowing the control unit to make decision as to overlap of the extents of the input/output processings to thereby effectuate exclusive control on an extent-by-extent basis.

BACKGROUND OF THE INVENTION

[0001] The present invention relates to a data storage system coupled orconnected to a plurality of host processors. More particularly, theinvention is concerned with a technology which can effectively beadopted for enhancing efficiency of exclusive control for the processingof stored data.

[0002] In general, there exist a plurality of files in one volume set upin a magnetic disk drive or device. When a file in a given volume isbeing used by a given host processor, the volume containing that fileassumes a device busy state. As a result of this, access of other hostprocessor to the other file contained in the given volume is forced towait for releasing of the volume from the device busy state. This isbecause such exclusive use is effectuated that when one host processoris using one volume, any other host processor is disabled to use thatvolume.

[0003] With the access control scheme mentioned above, there arises aproblem that when a plurality of files exist on a given volume, filesother than that for which the exclusion is to be effectuated areunnecessarily subjected to the exclusion, which leads to degradation offile utilization efficiency. For solving the problem mentioned above,there has been proposed such approach that a control memory is providedin a magnetic disk control unit for storing information indicating on afile-by-file basis whether or not individual files are being used,wherein the use statuses of the files are checked by a host processorsystem by reading the above-mentioned information from the correspondingcontrol memory, as disclosed, for example, in JP-B-1-15899. In the fileaccess control scheme disclosed in JP-B-1-15899, the exclusive controlis performed on a logical-file basis. Consequently, when sharing of asame file is desired, e.g. when a same file is to be shared by two hostprocessors only for read operation, such sharing of the same file isimpossible because of the exclusion on a file-by-file basis.

[0004] Further, JP-A-7-200179 discloses a scheme according to which aphysical volume is partitioned into a plurality of subvolumes. With thevolume management scheme disclosed in JP-A-7-200179, the exclusivecontrol can be carried out on a subvolume basis. In that case, thesubvolume itself has to be created upon formatting of the disk. Further,the exclusive control of the subvolumes is performed by the hostprocessor by confirming or checking the use status of the subvolumes onthe basis of information held by an external storage.

[0005] In the conventional systems described above, for effectuating theexclusive control on the basis of files contained in a physical volumeor on a subvolume basis, it becomes necessary that the host processingsystem reads from the magnetic disk device the information indicatingwhether or not the files or subvolumes are being used, to thereby checkwhether the file or subvolume of concern is being used or not, which inturn means that the host processing has to be imparted with an especialfunction for the exclusive control. For realizing such exclusivecontrol, alteration or modification of both host software and the serverstorage control unit becomes necessary.

SUMMARY OF THE INVENTION

[0006] In the light of the state of the art described above, it is anobject of the present invention to provide a storage system which iscapable of performing exclusive control of input/output processingrequests on the basis of files (i.e., on a file-by-file basis) which arecontained in a volume in the case where individual files contained inthe volume are to be shared by a plurality of systems, without need forimparting to the host processing system and/or host software thefunction for checking whether the file or files stored in a serverstorage unit is being used or not.

[0007] In view of the above and other objects which will become apparentas the description proceeds, there is provided according to an aspect ofthe present invention a storage system which is comprised of a controlunit incorporating a control memory, wherein information concerning theextent (range) of an input/output processing request (hereinafter alsoreferred to as the input/output processing request extent) which istransferred from a given one of plural host processors to the controlunit upon issuance of the input/output processing request from theformer is stored in the control memory with a view to realizing theexclusive control for a plurality of input/output processing requestsissued from a plurality of host processors to one logical device bymaking use of the extent information mentioned above. When aninput/output processing request is newly issued, decision is made as towhether or not any input/output processing request whose extent overlapswith that of the newly issued input/output processing request is beingexecuted. Unless overlap of the extents is found, the input/outputprocessing as requested currently is executed continuously. On the otherhand, when the extent overlap is found, the newly issued input/outputprocessing request is stored in the control memory as the input/outputprocessing request waiting for execution.

[0008] In the control memory incorporated in the control unit,identifiers defined inherently to the individual input/outputprocessings (hereinafter referred to as the input/output processingrequest identifiers), respectively, and identifiers of paths by way ofwhich the input/output processing requests are transferred to thecontrol unit (hereinafter also referred to as the path identifiers) arestored on a request-by-request basis. The extent information of theindividual input/output processing requests is stored in correspondenceto the input/output processing request identifiers, respectively.Further, for the input/output processing request for which overlap ofthe extent is decided and which is thus forced to wait for execution,the information indicating occurrence of wait-event is stored incorrespondence to the relevant input/output processing requestidentifier.

[0009] Furthermore, in the storage system according to the presentinvention, the wait-event occurrence information stored in the controlmemory is referred upon completion of the input/output processing forthe preceding request. When the input/output request waiting forexecution in succession to the preceding input/output processing requestexists, a request for reconnection of the input/output processingawaiting the execution is issued to the host processor.

[0010] Besides, in a preferred mode for carrying out the presentinvention, service equipment having a function for transmittinginformation to the control memory incorporated in the control unit maybe employed for allowing the control unit to inhibit the logical devicefrom the aforementioned exclusive control on the extent-by-extent basiswhen it is indicated by the service equipment that the extent exclusivecontrol on the logical-device basis is not to be performed.

[0011] The above and other objects, features and attendant advantages ofthe present invention will more easily be understood by reading thefollowing description of the preferred embodiments thereof taken, onlyby way of example, in conjunction with the accompanying drawings, beingappreciated that many modifications and variations of the presentinvention are possible in the light of the teachings disclosed herein.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012] In the course of the description which follows, reference is madeto the drawings, in which:

[0013]FIG. 1 is a block diagram showing schematically a generalarrangement of a storage system according to an embodiment of thepresent invention;

[0014]FIG. 2 is a view for illustrating, by way of example, commandstransferred between host processors and a control unit;

[0015]FIG. 3 is a view illustrating a structure of logical devicecontrol tables stored in control memories of a control unit in thestorage system according to an embodiment of the present invention;

[0016]FIG. 4 is a view illustrating a structure of input/outputprocessing control tables stored in the control memories of the controlunit;

[0017]FIG. 5 is a view illustrating a structure of a path groupidentifier table stored in the control memories of the control unit;

[0018]FIG. 6 is a view illustrating a structure of an extent-basedexclusive-use suppression control table stored in the control memoriesof the control unit;

[0019]FIG. 7 is a flow chart for illustrating a processing procedureexecuted according to the teachings of the invention in case aninput/output processing request containing extent information is issued;

[0020]FIG. 8 is a flow chart for illustrating a processing procedure forexecuting an extent-based exclusive control according to the presentinvention; and

[0021]FIG. 9 is a flow chart for illustrating a process for restartingan input/output processing request forced to wait for execution by theexclusive control according to the present invention.

DESCRIPTION OF THE EMBODIMENTS

[0022] The present invention will be described in detail in conjunctionwith what is presently considered as preferred or typical embodimentsthereof by reference to the drawings. In the following description, likereference characters designate like or corresponding parts throughoutthe several views.

(A) General Arrangement of Storage System

[0023] Referring to FIG. 1, the storage system according to anembodiment of the present invention includes a plurality of hostprocessors (#1, #2) 10 for performing arithmetic operations or the likeby processing information or data, channels 11 for performinginput/output control such as control of data transfer, an array-typeexternal storage unit 14, and a control unit 12 which is in charge ofcontrolling the components or units mentioned above. The storage systemnow under consideration is so arranged that read/write data operationfor a logical device 143 set up in the array-type external storage unit14 is carried out in response to a command issued by a given one of thehost processors 10 by way of the relevant channel 11 and a relevant hostadaptor 122, a cache memory 121 and a disk adaptor 123 which areincorporated in the control unit 12.

[0024] The control unit 12 incorporates therein control memories 124which are adapted to store control information used for carrying outcontrols described hereinafter and is provided with service equipment 13which serves for a function for transmitting external commands to thecontrol memory 124. Each of the host adaptors 122 incorporated in thecontrol unit 12 is designed to control the data transfer with thechannels 11. On the other hand, each of the disk adaptors 123 alsoincorporated in the control unit 12 is designed to control theread/write data operation for the logical device or devices 143 set upover a plurality of physical devices 142 provided in the array-typeexternal storage unit 14. The host adaptor 122 and the disk adaptor 123perform read/write data operation for the cache memory 121. Thus, datatransfer between the host adaptor 122 and the disk adaptor 123 can berealized through the medium of the cache memory 121. In the controlmemory 124, there is stored control information in the form of logicaldevice control tables 30, input/output processing control tables 40, apath group identifier table 50 and an extent-based exclusive-usesuppression control table 60, etc., which will be described in detailhereinafter. The host adaptors 122, the cache memories 121, the controlmemories 124 and the disk adaptors 123 are connected or coupled to buses125, respectively, as can be seen in FIG. 1.

[0025] Now, description will be directed to operation in general of thesystem implemented in the configuration described above. In the readdata operation, a read request issued from a given one of the hostprocessors 10 is first received by the relevant host adaptor 122,whereupon the host adaptor 122 checks the cache memory 121 as to whetheror not the data as required is available in the cache memory 121. Incase the required data exists in the cache memory, the host adaptor 122transfers the data to the relevant host processor 10 from the cachememory. On the other hand, unless the required data is available fromthe cache memory 121, the host adaptor 122 requests the disk adaptor 123for reading the required data from the logical device 143 installedinternally of the array-type external storage unit 14. After the diskadaptor 123 has stored once the required data in the cache memory 121,the host adaptor 122 transfers the required data to the host processor10.

[0026] In the write data operation, a write request issued by a givenone of the host processors 10 is received by the host adaptor 122incorporated in the control unit 12. Subsequently, the host adaptor 122writes the received data in the cache memory 121 and sends a writecommand end message indicating completion of the write request to thehost processor 10. The disk adaptor 123 transfers the data storedtemporarily in the cache memory to the logical device 143 to be writtenat a location indicated by the write request.

[0027] The array-type external storage unit 14 is constituted by aplurality of array groups 141, wherein each of the array groups isconstituted by a plurality of physical devices 142. The logical devices143 accessed by the host processor on a device-by-device basis are setup across a plurality of physical devices 142. By virtue of sucharrangement, even when a plurality of processing requests are issued toone and the same logical device 143, these processing requests can beprocessed, respectively, by the relevant physical devices 142 inparallel, so long as the extents of the plural input/output processingrequests are destined for the physical devices which differ from oneanother. Thus, the processing efficiency can be enhanced.

[0028]FIG. 2 is a view for illustrating a heading or leading portion ofa CCW chain (Channel Command Word chain) with which channel requests forreading data as an example of the instruction or commands and datagroups transferred between the host processor 10 and the control unit 12by way of the channel 11. Referring to FIG. 2, a command “Define Extent”serves for defining the range or extent of the input/output processingof a succeeding command, a cache access mode and the like. A command“Locate Record” validates or enables seek and search operations for atarget or object record, while a command “Read Data” designates readoperation of the relevant data. The extent information designated by thecommand “Define Extent” has heretofore been used for rejecting theexecution in case the succeeding input/output command is out of therange or extent. By contrast, according to the teachings of the presentinvention, the extent information is stored in the control memory 124for the exclusive control, which will be described later on.

(B) Logical Device Control Information Stored in Control Memory ofControl Unit

[0029]FIG. 3 is a view for illustrating logical device control tables 30stored in the control memories 124 incorporated in the control unit 12in the system according to the present invention. The number of thelogical device control tables 30 as provided may be equal to that of thelogical devices 143 controlled by the control unit 12, wherein each ofthe logical device control tables is affixed with a logical device IDnumber 301 as the identifier for identifying the relevant logicaldevice.

[0030] Upon issuance of an input/output processing request from a givenone of the host processors 10, an input/output processing managing area302 is allocated to the logical device control table relevant to theinput/output processing as requested. For identifying the input/outputprocessing, relevant one of the input/output processings is assignedwith the input/output processing control table ID number 303 which isthen stored in the input/output processing managing area 302.Additionally, for identifying discriminatively the host processor whichexecuted the input/output processing, there is stored in the relevantlogical device control table (30) a path group identifier or identifiers304 prescribed by the relevant host processor 10 for one or plural pathsets intervening between the individual host processors 10 and thecontrol unit.

(C) Input/Output Processing Control Information Stored in Control Memoryof Control Unit

[0031]FIG. 4 is a view showing input/output processing control tables 40designed for storing individual information of the input/outputprocessings, respectively, which are requested for the control unit 12.Each of the input/output processing control tables 40 is affixed withthe input/output processing control table ID number 303 as an identifierfor identifying the input/output processing. The input/output processingcontrol table ID number corresponds to the input/output processingcontrol table ID number 303 shown in FIG. 2. Stored in each of theinput/output processing control tables 40 is the extent information 401which is based on the command “Define Extent” sent from the hostprocessor 10.

[0032] The extent information 401 contains a start address and an endaddress of the relevant logical device determined on the basis of theextent of the input/output processing request designated by the command“Define Extent”, to thereby define the extent of the logical device overwhich the input/output processing is to be performed. The control unitof the storage system according to the present invention is so designedor programmed as to perform the exclusive control on the basis of theextent information 401. Consequently, when the extent information 401 ofa given input/output processing overlaps with that of the otherinput/output processing which is being currently executed, the giveninput/output processing is forced to wait for the start of executionthereof, which is referred to as occurrence of wait event. In this case,information concerning the relevant wait-event occurrence time 402 isstored in the input/output processing control table.

[0033] Further, upon execution of the input/output processing requestedby the host processor 10, decision is made as to whether this processingis activated initially or it has been forced to wait for execution bythe exclusive control and is executed by restarting. To this end, thereis provided the reconnection-relating information 403 in whichinformation indicating the reconnection is set when execution of aninput/output processing is to be restarted from the waiting state.

(D) Path Group Identifier Information Stored in Control Memory ofControl Unit

[0034]FIG. 5 is a view illustrating a structure of the path groupidentifier table 50 for acquiring the path group identifier to therebydetermine in which of the host processors the input/output processingrequest issued to the control unit originates. The path group identifiertable 50 is resident in the control memory 124 incorporated in thecontrol unit. More specifically, a number of areas equal to that of thepaths which interconnect the control unit and the host processors areprovided on the control memory 124, wherein one path group identifier304 can definitely be identified by one path identifier 501. To say inanother way, one-to-one correspondences are established between the pathidentifiers and the path group identifiers, respectively.

(E) Extent-Based Exclusive-Use Suppression Control Information Stored inControl Memory of Control Unit

[0035]FIG. 6 is a view for illustrating a structure of the extent-basedexclusive-use bypass or suppression control table 60 which table isreferred to when the exclusive control is to be suppressed or bypassedon a logical-device basis due to the extent designated by the serviceequipment 13 or by the command of the host processor. The extent-basedexclusive-use suppression control tables 60 are prepared in a numberequal to that of the logical device ID numbers 301. When theextent-based exclusive use is to be suppressed, information indicatingthe suppression is set in the relevant extent-based exclusive-usesuppression control information 601.

(F) Extent-Based Exclusive Control Operation

[0036] FIGS. 7 to 9 are flow charts for illustrating the exclusivecontrol performed on an extent-by-extent basis upon reception ofcommands for plural input/output processings for one volume from pluralhost processors by the host adaptors 122.

[0037] More specifically, FIG. 7 is a flow chart for illustrating aprocessing procedure executed when a command for input/output processingis received by the host adaptor 122 from the host processor.

[0038] If an extent exclusive control is not suppressed by a serviceequipment or a host, upon issuance of the input/output processingrequest from a given one of the host processors, decision is made in astep 702 as to whether or not the extent-based exclusive-use suppressioncontrol information 601 indicating that the exclusive control taught bythe present invention is to be evaded or suppressed for the logicaldevice to which the input/output processing request mentioned above isdirected has been set in the extent-based exclusive-use suppressioncontrol table 60 stored in the control memory 124 of the control unit bythe external service equipment or by other host processor. Whenbypassing or avoidance of the exclusive control is set, the processingproceeds to a step 703, whereupon the exclusive control is performed ona logical-device basis as in the case of the conventional techniquesdescribed hereinbefore, for thereby allowing the input/output processingas requested to be executed continuously (step 706). On the other hand,unless the bypassing or avoidance of the exclusive control is set, theprocessing proceeds to a step 704. In this step 704, it is decidedwhether the input/output processing request mentioned above is validatedby the reconnection or activated initially. The above decision can bemade on the basis of the reconnection-relating information 403 containedin the input/output processing control table 40 which is stored in thecontrol memory 124 of the control unit. In case the input/outputprocessing request is activated by the reconnection, the processingproceeds to a step 706 to continue execution of the input/outputprocessing.

[0039] On the other hand, when the input/output processing request isthe one activated initially, the logical device control table 30 islocked in a step 705, which is then followed by a step 707 where therelevant path group identifier is acquired by referring to the pathgroup identifier table 50 with the path identifier of the activatingpath. In succession, in a step 708, the input/output processing managingarea 302 of the logical device control table 30 for the relevant logicaldevice in which the path group identifier 304 is not registered issearched to thereby secure the input/output processing managing area 302in which the path group identifier has not yet been registered. In astep 709, the path group identifier 304 and the input/output processingcontrol table ID number 303 capable of identifying the input/outputprocessing are recorded to be used as the information for makingdecision as to which of the host processors the input/output processingrequest now concerned originates in.

[0040]FIG. 8 is a flow chart for illustrating a processing procedure forexecuting the extent-based exclusive control by storing the informationconcerning the extent (i.e., extent information) of the input/outputprocessing request received from a host processor in the input/outputprocessing control table 40 prepared on the control memory 124 and bymaking decision as to the overlap of the extent with that of otherinput/output processing. Referring to the figure, decision is made in astep 801 as to whether or not the input/output processing requesttransferred from the host processor contains information concerning theextent (extent information). When the extent information is transferred,the transferred extent information is recorded as the extent information401 of the relevant input/output processing control table ID number 303stored in the logical device control table 30 (step 802). On the otherhand, when no extent information is available, the start address and theend address of the relevant logical device are recorded as the extentinformation 401, whereupon the exclusive control is executed with thewhole volume being regarded as one extent (step 803).

[0041] Subsequently, in a step 804, decision is made for the relevantlogical device whether or not the extent information 401 of theinput/output processing to be executed overlaps with the extentinformation 401 for the other input/output processing request. Whenoverlap is found, information of the wait-event occurrence time 402 isrecorded in the input/output processing control table 40 for theprocessing which is forced to wait for (step 805), whereon the logicaldevice control table 30 is released from the locked state in a step 806.Unless overlap is found, the logical device control table 30 isimmediately unlocked in the step 806.

[0042] When the overlap is determined in a step 807, thereconnection-relating information 403 is set in the input/outputprocessing control table 40 in a step 808, whereon interconnection withthe host processor is cleared in a step 809. Then, the extent-releaseawaiting state is validated until the reconnection request is issuedwith the relevant extent being released (step 810). By contrast, when nooverlap is decided in the step 807, the input/output processing isexecuted in a step 811.

[0043] In case-the input/output processing command is a read datacommand, then, data is read out from the cache memory when the datawhich overs the range of the input/output processing request is residenton the cache memory. By contrast, unless the data covering the range orextent of the input/output processing request is available from thecache memory, the data is read out from the arrayrtype external storageunit 14. Upon completion of the input/output processing (read processingin this case), the procedure proceeds to the input/output terminationprocessing. By virtue of the exclusive control based on the extentinformation according to the present invention, a plurality ofinput/output processings can be executed for one and the same logicaldevice so long as no overlap occurs in respect to the extent. Further,when these plural input/output processings are to be executed for themutually different logical devices and when relevant data is unavailablefrom the cache memory (cache miss event) the data reading from theplural physical devices of the array-type external storage can beexecuted in parallel. However, when the physical devices are being usedfor executing the input/output processing for the same logical device orfor the other logical device, the device-busy state is set.

[0044] In case the input/output processing command is a write command,data covered by the range or extent of the input/output processingrequest is written in the cache memory. Thereafter, the data is writtenin the logical device by the control unit, being transferred from thecache memory. Upon completion of the input/output processing, theprocedure proceeds to the input/output termination processing.

[0045]FIG. 9 is a flow chart for illustrating the processings involvedwhen the input/output processing procedure is terminated through thehost adaptor 122. In a step 901, the logical device control table 30 islocked, which is then followed by a step 902 where the path groupidentifier 304 set in the relevant input/output processing managing area302 is deleted for thereby allowing the relevant extent to be released.

[0046] In a step 903, for the logical device for which the input/outputprocessing is to be terminated, decision is made as to presence of theinput/output processing which is in the waiting state because of overlapof the extent with that of the input/output processing to be terminatedthrough comparison with the extent information 401 placed in theinput/output processing control table 40 corresponding to the otherinput/output managing area for the logical device mentioned above and bychecking whether or not the wait-event occurrence time 402 is stored.Unless the wait-event occurrence time 402 is recorded in theinput/output processing control table 40 or unless overlap of the extentoccurs even when the wait-event occurrence time is recorded, the logicaldevice control table 30 is released from the locked state in a step 906,whereupon the processing procedure comes to an end.

[0047] In case the wait-event occurrence time 402 is stored and when theinput/output processing control table 40 for which the extent overlapwith the input/output processing to be terminated exists, one of theinput/output processing control tables in which the wait-eventoccurrence time 402 is oldest is selected in a step 904 for allowing theinput/output processing managing area 302 of the selected input/outputprocessing control table 40 to be made active. In a step 905, the hostprocessor to be reconnected is specified on the basis of the path groupidentifier 304 placed in the corresponding input/output processingmanaging area 302 corresponding to the selected input/output processingcontrol table 40, whereupon request for reconnection is issued to thespecified host processor while the logical device control table 30 isreleased from the locked state in a step 906. Subsequently, theinput/output processing activated through the reconnection is executedin succussion.

(G) Avoidance of Extent Exclusive Control

[0048] When avoidance of the exclusive control on the extent-by-extentbasis described previously is commanded by the service equipment havingthe function for performing input/output operation on the control memory124 of the control unit or designated by the control information sent tothe control unit from the host processor, the extent-based exclusivecontrol is not carried out for the logical volumes designated by thecommand. In that case, the input/output processing is performed inaccordance with the conventional logic.

[0049] As will now be appreciated from the foregoing description, in thestorage system according to the present invention, exclusive control forplural input/output processing requests issued for one logical devicefrom the host processors is performed on the basis of the range orextent of the input/output processing requests. By virtue of thisfeature, when the relevant data exists on the cache memory of thecontrol unit and thus the access to the physical device is unnecessaryor when access is made to the data on one and the same logical deviceset up over the different physical devices of the array-type externalstorage unit, efficiency of data input/output operation can be enhancedsurprisingly, whereby throughput of the system as a whole can beimproved significantly.

1. A storage system, comprising a control unit coupled to a plurality ofhost processors for receiving therefrom a plurality of input/outputprocessing requests each containing a command designating an extent ofthe input/output processing request to thereby control data transfersbetween said host processors and a plurality of storage devices on thebasis of the commands of said input/output processing requests, saidcontrol unit including memories for storing control information for saidinput/output processing requests on a request-by-request basis, saidplurality of storage devices being coupled to said control unit, whereinlogical devices are set up across said plurality of storage devices,wherein upon reception of a newly issued input/output processingrequest, said control unit stores the extent of said newly issuedinput/output processing request in said memory for executing said newlyissued input/output processing request provided that any otherinput/output processing request whose extent overlaps with that of saidnewly issued input/output processing request is not resident in saidmemory, whereas when other input/output processing request whose extentoverlaps with that of said newly issued input/output processing requestis stored in said memory, information indicating that said newly issuedinput/output processing request is forced to wait for execution thereofis stored in said memory.
 2. A storage system according to claim 1,wherein when the extents of a plurality of input/output processingrequests for one of said logical volumes are covered by mutuallydifferent storage devices, respectively, operation of reading data fromsaid storage devices are carried out in parallel in response to saidplurality of input/output processing requests.
 3. A storage systemaccording to claim 1, wherein said control unit is provided with serviceequipment having input/output function for the control memoryincorporated in said control unit, information indicating whetherexclusive control is to be performed or not on the basis of the extentof said input/output processing request is stored in said control memoryunder the command of said service equipment or said host processor, andwherein upon issuance of a new input/output processing request, saidcontrol unit selects on the basis of said information either theexclusive control based on the extent of said new input/outputprocessing request or the exclusive control based on logical volumes. 4.A storage system coupled to a plurality of host processors, comprising:an external storage; and a control unit for controlling transfer ofinformation between said host processors and said external storage,wherein arrangement is made such that device busy state is preventedfrom occurrence even when a plurality of commands which do not overlapin respect to extents of input/output processing requests are receivedfrom said plurality of host processors for a same logical device.
 5. Astorage system according to claim 4, wherein arrangement is made suchthat said device busy state is prevented from occurrence when saidplurality of commands which exhibit no overlap in respect to the extentsof the input/output processing requests are received for a same filerather than said same logical device.
 6. A storage system according toclaim 4, wherein said host processor is imparted with no function forchecking whether or not files stored in said storage device are beingused.
 7. A storage system according to claim 4, wherein in said externalstorage, one logical device is setup over a plurality of physicaldevices.
 8. A storage system according to claim 7, wherein arrangementis made such that device busy state can occur when said physical deviceis being used.
 9. A storage system coupled to a plurality of hostprocessors, comprising: an external storage; and a control unit forcontrolling transfer of information between said host processors andsaid external storage, wherein exclusive control for a plurality ofinput/output processing requests issued for a same logical device fromsaid plurality of host processors is performed by making use of extentof the input/output processing request contained in commands issued byhost processors.
 10. A storage system according to claim 9, whereinarrangement is made such that said exclusive control can be suppressedeither by service equipment coupled to said control unit or by said hostprocessors.
 11. A control method in a storage system coupled to aplurality of host processors, said storage system having an externalstorage device and a control unit for controlling transfer ofinformation between said host processors and said external storagedevice, said method comprising: a first step of issuing, from a hostprocessor, a first command including specification of a logical deviceand an extent of an input/output request; and a second step of issuing,from a host processor, a second command including specification of alogical device and an extent of an input/output request, wherein evenwhen said first and second steps exist, a device busy state is preventedfrom occurrence though a same logical device is specified in both thecommands unless said extents of said input/output requests of said firstand second commands overlap on each other.
 12. A control methodaccording to claim 11, wherein even for a same file rather than saidsame logical device, said device busy state is prevented fromoccurrence.
 13. A control method according to claim 11, wherein saidhost computer is imparted with no function for checking whether or notfiles stored in said storage device are being used.
 14. A control methodaccording to claim 11, wherein in said external storage device, said onelogical device is setup over a plurality of physical devices.
 15. Acontrol method according to claim 14, further comprising a third step ofissuing said device busy state when a physical device is being used. 16.A control method in a storage system coupled to a plurality of hostprocessors, said storage system having an external storage device and acontrol unit for controlling transfer of information between said hostprocessors and said external storage device, said method comprising: afirst step of issuing, from a host processor, a command for suppressingexclusive control; a second step of issuing, from a host processor, afirst command including specification of a logical device and an extentof an input/output request; and a third step of issuing, from a hostprocessor, a second command including specification of a logical deviceand an extent of an input/output request, wherein even when said first,second and third steps exist, a device busy state occurs in spite ofthat said extents of said input/output requests of said first and secondcommands do not overlap on each other.
 17. A control method in a storagesystem coupled to a plurality of host processors and a serviceequipment, said storage system having an external storage device and acontrol unit for controlling transfer of information between said hostprocessors and said external storage device, said method comprising: afirst step of issuing, from a service equipment, a command forsuppressing exclusive control; a second step of issuing a first commandincluding specification of a logical device and an extent of aninput/output request; and a third step of issuing a second commandincluding specification of a logical device and an extent of aninput/output request, wherein even when said first, second and thirdsteps exist, a device busy state occurs in spite of that said extents ofsaid input/output requests of said first and second commands do notoverlap on each other.
 18. A control method according to claim 17,wherein said second and third steps are issued by said host processors.19. A recording medium storing a computer readable program executing thecontrol method according to claim
 11. 20. A recording medium storing acomputer readable program executing the control method according toclaim
 16. 21. A recording medium storing a computer readable programexecuting the control method according to claim
 17. 22. A computerreadable program on a recording medium executing the control methodaccording to claim
 11. 23. A computer readable program on a recordingmedium executing the control method according to claim
 16. 24. Acomputer readable program on a recording medium executing the controlmethod according to claim 17.